It has long been known to manufacture and distribute pressure-sensitive adhesive labelstock for labels by providing a facestock material for the label or sign, backed by a layer of pressure sensitive adhesive (“PSA”), which in turn, generally is covered by a release liner or carrier. The liner or carrier protects the adhesive during shipment and storage and allows for efficient handling of an array of individual labels after the labels are die-cut and the matrix is stripped from the layer of facestock material, and up to the point where the individual labels are dispensed in sequence on a labeling line, for example when applied to a substrate. During the time from die-cutting to dispensing, the release liner or carrier remains uncut and may be rolled and unrolled for storage, transit, and deployment of the array of individual labels carried thereon.
Failure of the labels to reliably dispense from the release liner or carrier for application to the substrate is typically characterized by the label following the carrier around a peel plate without dispensing, releasing, or “standing-off” from the carrier. Such failure to dispense is believed to be associated with excessive release values between the label facestock material and the liner. Dispensability also is dependent upon the stiffness of the facestock, wherein insufficient stiffness results in a failure of the facestock to dispense from the carrier. Failure to dispense due to lack of label stiffness may also be characterized by the wrinkling of the label at the dispensing speed as it is transferred from the carrier to the substrate. Another particular need in labeling applications is the ability to apply polymeric-film labels at high line speeds, since increased line speed has obvious cost saving advantages.
There is also a need for down-gauging of label films in order to improve the cost performance ratio of labelstock. Down-gauging of label films to make them thinner is associated with reduced strength and reduced stiffness of the film. A disadvantage of down-gauging of films is that the stiffness in the machine direction of the film will become too low to guarantee good dispensing of the labels. This problem has been addressed by stretch orienting the film in the machine direction (MD) and/or the cross direction (CD), or by utilizing materials having a higher modulus of elasticity and, hence, higher stiffness.
Polypropylenes, and in particular biaxially oriented polypropylene (BOPP), have been utilized successfully in down-gauging applications since polypropylene is relatively inexpensive and exhibits sufficient stiffness to dispense well. However, polypropylenes in general exhibit relatively high tensile modulus values in both machine-direction and cross-direction which results in labels that are not very conformable, resulting in unsatisfactory labeling of contoured substrates. Additionally, polypropylenes are not easily printable with UV based inks, which are most commonly used to print on pressure sensitive adhesive labels.
When films with incompatible polypropylene-polyethylene (PP-PE) blends are used, resulting films tend to be hazy and not clear. Furthermore, when the PP-PE films are stretched to be machine direction oriented (MDO), an outer surface of the films tend to have significant surface roughness after the stretch orienting process. Surface roughness of an outer surface of the films plays a huge role in optical properties of the films such as MD gloss, CD gloss, haze and clarity. As such, these PP-PE blended MDO films have poor film optics. In particular, if surface features of the films have a height that approaches the wavelength of visible light, the features will scatter light and reduce film optics.
Current PP-PE blended MDO films are not sufficiently clear, and are significantly hazy. This haziness can be reduced by applying a lacquer coating to the outer surface of the film. However, such top-coatings require additional processing steps and cost; and even with such top-coatings, it has been observed that print aesthetics, such as color saturation, are not satisfactory. Unsatisfactory print aesthetics is especially apparent when printing with metallure inks, which do not “pop” from the background created by the surface of the MDO films.
Therefore, a need exists for high optical, clear MDO films having high gloss that provide satisfactory print aesthetics and have sufficient stiffness for high speed dispensing.